fix docker deployment

README.md

@@ -33,6 +33,7 @@ Same Compose layout as the site app. On the HQ host: UI **:80**, API debug **:18
 ```bash
 cp docker/.env.example .env
 # set SECRET_KEY, DB_PASSWORD, BOOTSTRAP_ADMIN_PASSWORD
+# optional: FRONTEND_PORT=8080 if host :80 is busy
 docker compose up -d --build
 ```